I generally drop things I hate. The main drama that I didn't like at all but finished was Coffee Prince, but I was very new to kdramas at the time and kept waiting for it to get better. I swore off kdramas and mostly stuck to jdramas for a while after because of it. I also really didn't like Kono yo no Hate or Proposal Daisakusen much. There have been dramas I finished that I just found mediocre or weren't really like my tastes, like Love Shuffle. I tend to drop those nowadays too.

I have, however, finished movies I didn't like, like 200 Pounds Beauty and a few others.
Mmm... let me think.

I think Drinking Solo was like that. I watched it just because I was used to going back home and watching something and I happened to watch 4 different shows that lined up 2 episodes a day nicely... I didn't particularly like the show, though. 
The other one was Angel Eyes. It was my second drama, so I naturally wanted to see how it ends.
I think Playful Kiss was one of those, too. I think that I watched it because it was one of the few dramas that were available for download from Netflix and I had it on my phone while travelling.

I don't know if I could say that I genuinely hated any of them, though.
Hmm, the most drama i love to hate would be the Temptation of Wife. I hated most of the characters, i am annoyed because of the weak lead but i just cant stop watching it.
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Emergency Couple 
High Society
Warm and Cozy
Goblin
Falling for Innocence 
Doctors
The Heirs
You're Beautiful
High society
The heirs
Playful Kiss

Temperature of Love, watched only 4 eps of this and can't even get into it at all even during their kiss scene - dropping this. My Golden Life was boring me too for the first 2 episodes, only watched it to see what the hype was about

forgot to put Healer there, the first half was meh but later half of the show was much better (ep 8+)

Drama I hated but still watched to completion anyway:   Hwarang  and  Saimdang Light's Diary

Boys over Flowers - Technically i only liked Kim Bum and Kim So Eun's character. I couldn't care less for the main couple.

 iamgeralddd:
Coffee prince.. i remember fast forwarding for the last few episodes...

Thanks God I'm not the only one

Hi! School -Love On

I really can't understand how I finished this drama xD

I don't really enjoy school dramas in general but I still watched it for Sungyeol's sake. 

the love story is so cringe worthy lol and it's toooo 'childish'? for me. 

Goblin-It was SUPER hyped that I couldn't wait to watch it! I start watching the drama I don't know why but at some point it didnt make anymore sense, I feel like the plot was lost!!! I honestly felt robbed while watching this drama, complete waste of time.

The Bride of Habaek-Probably the worst drama I've ever watched in the last 6 years. It's really bad, I've litteraly fell asleep while watching this!!! The story does not make any sense, I still don't know why I watched the whole damn thing!!!!!!!

And I regret watching the whole 16 EPS of these two!!!!

There definetly others tho.

 EstherT:
The Bride of Habaek-Probably the worst drama I've ever watched in the last 6 years. It's really bad, I've litteraly fell asleep while watching this!!! The story does not make any sense, I still don't know why I watched the whole damn thing!!!!!!!

omg, i forgot this.  i totally empathise!!!